Modern power capacitors are characterized by very great energy density, which makes it important to limit the consequences of a fault. As primary protection against capacitor explosions, fuses are used in conventional power capacitors. There are two accepted methods of providing power capacitors with fuses:
a) by means of internal fuses, and PA1 b) by means of external fuses. PA1 a) the power capacitor is composed of a plurality of parallel-connected strings of capacitor elements, PA1 b) each string comprises a plurality of series-connected capacitor elements, PA1 c) the parallel strings are interconnected only at their end points, and wherein dielectrics and electrodes included in the capacitor element are arranged such that the electrodes are welded together in case of breakdown and a solid short circuit without the risk of partial discharge or restriking occurs.
Protection of power capacitors by means of internal fuses is space-demanding and renders production expensive since each capacitor element is series-connected with a fuse. However, in relation to the constructionally simpler protection using external fuses, protection by means of internal fuses entails technical advantages since a fault leads to disconnection of the faulty element, which results in very small capacitance changes and increased availability of a power capacitor with internal fuses.
Currently used power capacitors have inherent limitations which can be derived from the respective fuse technique:
Power capacitor units with internal fuses require a certain number of parallel-connected capacitor elements in each group, which limits the maximum unit voltage to approximately 9 kV. High-voltage capacitor banks must therefore be composed of a large number of series-connected groups.
Power capacitors with external fuses have poor protective function at currents higher than 30 A, which limits the maximum unit current. In addition, a certain number of parallel-connected capacitor units in each group are required. Power capacitors protected by means of external fuses must therefore be connected in few series-connected groups with a relatively large number of parallel-connected capacitor units in each group.
Fuse-free power capacitor designed according to the invention eliminate the above-mentioned limitations, and thus, while utilizing the invention, power capacitors can be designed in the most economical way in all applications.